The present invention relates to a cylinder head gasket placed between two members, such as a cylinder head and a cylinder block of an engine to seal therebetween. More specifically, even when the members on both sides are rubbed against each other and misaligned due to an external factor, such as a heat deformation of the members, the surface pressure on the end portion of a bore can be controlled not to rise, and indentation generated at the members can be reduced.
The cylinder head gasket is tightened by head bolts and seals fluid, such as combustion gas, oil, and coolant water in a state of being placed between the cylinder head and the cylinder block (cylinder body) of an automobile engine.
Also, as the weight and size of an engine have been reduced recently, the engine tends to have lower rigidity. Accordingly, when a large seal surface pressure is provided on the nearest part of the cylinder bore in order to assure a seal quality during the sealing of the cylinder head gasket, the cylinder bore is deformed because the engine member has lower rigidity. When the cylinder bore is deformed, a seal method, such as a bead or a folded portion, does not function well, and an adequate seal quality can not be obtained.
In order to provide an excellent seal quality by reducing the number of laminated plates, usage of the material, and the thickness of a whole gasket, and also by increasing the tightening pressure of the rim of a cylinder to the highest, metal gaskets, such as those shown in Japanese Patent Publications No. 8-121597 and No. 10-213227, form a wide folded portion (grommet portion) by directly folding back a secondary plate at the rim of the cylinder, and provide a full bead in two sheets of main plates which clamp the secondary plate. The full bead has a projection on the secondary plate side, and comes together with the folded portion.
However, in this kind of cylinder head gasket, the rim of the cylinder has the highest tightening pressure (seal pressure), so that the deformation of the cylinder bore can be accelerated. Also, the folded portion is directly folded back, and the folded diameter of the folded portion is small, thereby easily creating a crack.
In view of the problems described above, an object of the present invention is to provide a cylinder head gasket which can provide an excellent seal quality around the cylinder bore, and also can reduce the indentation around the cylinder bore which is generated at the engine member.
Further objects and advantages of the invention will be apparent from the following description of the invention.